1. Field of the Invention
This invention relates to a new process for the production of microcellular or foamed moldings wherein the reaction mixture--to be introduced into closed molds--is based on organic polyisocyanates and compounds containing isocyanate-reactive groups having as their main components specific compounds containing ammonium carbonate and/or ammonium bicarbonate groups, as described in more detail hereinafter, and to compounds suitable for carrying out this process.
2. Description of the Prior Art
It is known that carbonates and/or bicarbonates (hydrogen carbonates) of aliphatic mono- or polyamines can be produced from those amines, carbon dioxide and water. Crystalline compounds which are solid at room temperature and which are either insoluble or substantially insoluble in polyhydroxyl compounds, of the type normally used in the production of polyurethanes, are formed in these known processes. These crystalline compounds may be reacted with compounds containing isocyanate groups to form relatively high molecular weight compounds containing urea groups. Thus, U.S. Pat. No. 3,425,964 describes the hardening of polyurethane resins with solid amino carbonates, which can be stored indefinitely at 25.degree. C., and also the production of foamed products from those reactants. In this case, the poor solubility and the resulting poor reactivity of the amino carbonates are utilized by initially applying the reaction mixture to a steel plate and subsequently effecting formation of the foam structure at elevated temperatures with release of the carbon dioxide and crosslinking with the released amine. Similar processes are described in published Japanese Patent Application No. 92 010 (Application No. 72 13 068 filed 17.12.1968) and in published Japanese Patent Application No. 98 186 (Application No. 50-052 175 filed 3.9.1973).
Apart from these very special prior art processes, the poor solubility of the known carbonates and bicarbonates of organic polyamines in the starting materials used for the production of polyurethane plastics must be regarded as a serious disadvantage because satisfactory compatibility of the reactants is generally an essential requirement for the production of high-quality polyisocyanate polyaddition products. This is very probably the reason why the known aminocarbonates which are solid at room temperature have never been used in the practice as starting materials for the production of polyurethane plastics.
New compounds containing isocyanate-reactive groups have now surprisingly been found wherein the isocyanate-reactive groups are at least partly ammonium carbonate or ammonium bicarbonate groups of the type formed by the reaction of aliphatically bound primary or secondary amino groups with carbon dioxide and water. The new compounds are liquids which are stable in storage at room temperature and react off spontaneously with organic polyisocyanates with release of the carbon dioxide. The (co-)use of these compounds according to the invention, which are described in detail hereinafter, in the production of polyisocyanate polyaddition products (polyureas or polyurethane-ureas) affords a number of remarkable advantages, particularly in the production of microcellular or foamed moldings based on the above-mentioned starting materials.
In the production of polyurea-based microcellular moldings, i.e. moldings of which the density is about at least 10% and preferably 20 to 40% below the density of a corresponding, solid molding, the co-use of the new compounds provides above all for satisfactorily controllable metering of the blowing agent (the carbon dioxide released). In addition, the new compounds according to the invention are eminently suitable for the production of foamed polyurethane-urea moldings having a compact surface skin, i.e. moldings having a gross density of more than 40% and generally 45 to 85% below the density of a corresponding, solid molding. In the production of foamed moldings by the conventional process, particularly using organic blowing agents, so-called dwell zone markings often become visible because the reaction mixture does not begin to foam immediately. In addition, an often inadequate compatibility of the reactants is reflected in the form of streaks visible on the molding. These unfavorable phenomena can also be eliminated by the co-use of the compounds according to the invention because they react spontaneously with the polyisocyanate component with elimination of carbon dioxide so that no visibly marked dwell zones can be formed. Further, because of the liquid nature of the reactants, they may be more homogeneously mixed, thereby avoiding the formation of any streaks. Accordingly, the co-use of the compounds according to the invention in the production of moldings of the type in question, even in very low concentrations, often brings about a significant improvement in the surface of the moldings, by virtue of which homogeneous lacquer finishes can be obtained, for example by immersion lacquering of the moldings.